Butadiene is an important basic raw material used in the chemical industry and is a monomer used in a greatest amount among monomers used in the synthetic rubber industry. It is also an important intermediate used for the production of synthetic rubber and organic chemical raw material. Butadiene is widely used in synthesizing styrene butadiene rubber, cis-butadiene rubber, nitrile butadiene rubber, chloroprene rubber and ABS resin, etc.
Currently, butadiene is obtained mainly by extracting the by-product of naphtha cracking. However, with the development of light raw materials for ethylene and propylene, the yield of the cracking apparatus for naphtha is gradually reduced. Thus, the amounts of the extracted butadiene can not satisfy the ever-growing need of butadiene. There is an increased gap in the market for butadiene. Therefore, there is a need to develop a new process for the production of butadiene that is independent on alkene cracking. One feasible process is to prepare 1,3-butadiene by the oxidative dehydrogenation of butene, which is attractive by more and more people.
The catalysts currently used for catalyzing the oxidative dehydrogenation of butene mainly include ferrum based spinel catalyst, molybdenum based composite oxide catalyst and tin based catalyst. Two ferrum based catalysts, B-02 and H-198, had been developed in China in the 80's of the last century. Both have already been used in industry. The preferred advantages of the ferrite catalyst are little amount of oxygen-containing organic compounds in the by-product, and the waste water being readily treated. However, its disadvantages are low one-pass conversion rate, poor selectivity for butadiene, utilizing a large amount of water vapors as diluent gas, high energy consumption, and producing a large amount of waste waters.
The molybdenum based oxide catalyst exhibits high conversion rate and selectivity as compared with the ferrum based catalyst, and needs no water as a diluent gas in reaction. Thus, it has advantages in both the energy consumption and material consumption. The molybdenum based oxide catalyst generally comprises many metal components, its main active component is derived from bismuth molybdate, and other components are those derived from cobalt molybdate, ferrum molybdate and nickel molybdate as well as alkaline earth metal and alkali metal as co-catalysts [See, M. Niwa and Y. Murakami, J. Catal., 27, 26 (1972); A. P. V. Soares, L. D. Dimitrov, et al., Appl. Catal. A:Gen., 253, 191 (2003)].
Currently, there are two main methods for preparing the molybdenum based oxide catalyst, one is the co-precipitation method and the other is the direct drying method.
With respect to the direct drying method, U.S. Pat. No. 3,764,632 has disclosed a method for preparing a molybdenum based oxide catalyst by the direct drying method. Although the process of the method is simple, different metal elements in the catalyst are prone to isolate during drying because of the complicated catalyst components having different chemical properties. As a result, the components are not uniformly distributed in the catalyst, resulting in a complicated crystal phase structure, and, in turn, poor producing repeatability. In addition, the drying and firing steps of this method produce a large amount of waste gases containing nitrogen, chlorine, etc., troubling in the treatment of the waste gas.
With respect to the co-precipitation method, the current method for producing Bi/Mo/Fe composite oxide catalyst comprises to proceed with co-precipitation in a solution having an adjusted pH, obtaining a precursor. This method can enhance the activity of multi-component bismuth molybdate catalyst in a simple way. Although the co-precipitation method itself is simple, the metal ions may not be co-precipitated simultaneously or completely when preparing the catalyst by this method since different metal ions are precipitated at different pH values, resulting in the active ingredients not being uniformly distributed. In addition, the metal ions, such as cobalt ion, nickel ion and zinc ion, etc., may form a complex compound with the ammonium ion in the precipitating agent, which may be lost during filtration. Thus, it is difficult to precisely control the composition of the finally obtained catalyst, or a high cost is required to precisely control the composition of the finally obtained catalyst. As a result, the method is difficult to be practiced in an industrial scale. Furthermore, during preparation by the co-precipitation method, a lot of metal ion-containing waste water will be produced, which needs special treatment before discharge.
Mechanochemistry (or high-energy ball milling) is a method to prepare a superfine material. The mechanism of the mechanochemistry is to induce a chemical reaction or to induce change in composition, structure and property of the material by utilizing a mechanical energy, obtaining a new material. As a new technique, it can significantly reduce the activation energy of the reaction, decrease the size of crystal grain, greatly increase the activity of the powder, improve homogenous distribution of the particles, and enhance the interface binding among materials. It can also promote solid ion diffusion and induce a chemical reaction under low temperature to improve the properties, such as, degree of compaction, electric and thermal properties, of the material. Thus, it is a technique for preparing a material in an energy efficient and high efficient manner.
Considering the status of the prior art, there is still a need to develop a molybdenum based oxide catalyst used for preparing butadiene by the oxidative dehydrogenation of butene, which catalyst can not only exhibit high activity and selectivity, but also can be prepared in a relatively simple, controllable, and repeatable way with no active ingredients loss and reduced waste water and waste gas during preparation.